How thyroid disorders affect pregnancy?

Change in thyroid gland functions is called thyroid dysfunction. It can start during or after pregnancy in women who never had thyroid problems before. The reason for this condition is major changes in the levels of hormones made in the thyroid gland.

When the thyroid makes too much of the thyroid hormones T3 and T4, it is called overactive thyroid or hyperthyroidism. This problem also causes very low levels of thyroid-stimulating hormone (TSH), a hormone that tells the thyroid to make T3 and T4. This is because too much T3 and T4 in the body cause TSH production to shut down. An overactive thyroid greatly increases metabolism (how your body uses energy). It most often affects women ages 20 to 40, in their childbearing years. Hypothyroidism is when the thyroid gland does not produce enough thyroid hormones to meet the needs of the body. The thyroid is underactive.

Fortunately, hyperthyroidism during pregnancy is not very common so is the hypothyroidism. However, the symptoms may be overlooked because some can mimic the hormonal changes a woman has in a normal pregnancy, such as, feeling too warm, tired, or anxious. If left untreated, maternal hyperthyroidism poses a risk for both mother and baby. Pregnant women with uncontrolled hyperthyroidism can develop high blood pressure. There is also an increased risk of miscarriage, premature birth, and having a baby with a low birth weight.

There are 2 pregnancy-related hormones: estrogen and human chorionic gonadotropin (HCG), which may increase your thyroid levels. This may make it a bit harder to diagnose thyroid diseases that develop during pregnancy. However, your doctor will be on the look-out for symptoms that suggest the need for additional testing.

However, if you have pre-existing hyperthyroidism or hypothyroidism, you should expect more medical attention to keep these conditions in control while you are pregnant, especially for the first trimester.

Occasionally, pregnancy may cause symptoms similar to hyperthyroidism; should you experience any uncomfortable or new symptoms, including palpitations, weight loss, or persistent vomiting, you should, of course, contact your physician.

Untreated thyroid diseases during pregnancy may lead to premature birth, preeclampsia (a severe increase in blood pressure), miscarriage, and low birth weight among other problems. Therefore, it is important to talk to your doctor if you have had a history of hypothyroidism or hyperthyroidism so you can be monitored before and during your pregnancy, and to be sure that your medication is properly adjusted, if necessary.  

There may be 2 conditions, hyperthyroidism or hyperthyroidism.


Symptoms of hyperthyroidism may mimic those of normal pregnancy, such as an increased heart rate, sensitivity to hot temperatures, and fatigue. Other symptoms of hyperthyroidism include the following:


  • Irregular heartbeat
  • Heightened nervousness
  • Severe nausea or vomiting
  • Shaking hands (slight tremor)
  • Trouble sleeping
  • Weight loss or low weight gain beyond that expected of a typical pregnancy
  • Hypothyroidism:

Symptoms of hypothyroidism, such as extreme tiredness and weight gain, may be easily confused with normal symptoms of pregnancy. Other symptoms may include:

  • Constipation
  • Difficulty concentrating or memory problems
  • Sensitivity to cold temperatures
  • Muscle cramps

What is the cause of maternal hyperthyroidism and maternal hypothyroidism?

  • Hyperthyroidism:

A common cause of overactive thyroid (hyperthyroidism) in pregnant women is Graves’ disease. This disease occurs when your immune system becomes overactive and forms antibodies (immune proteins) that attack the thyroid. This causes the gland to enlarge and make too much thyroid hormone. Most women with Graves’ disease find out early that they have this disease and get treatment before they become pregnant.

Women with severe nausea and vomiting or those expecting twins may develop temporary hyperthyroidism. Called transient gestational thyrotoxicosis, this hyperthyroidism is due to high levels of a pregnancy hormone called human chorionic gonadotropin or HCG. Because it resolves by week 14 to 18 of pregnancy, women do not need antithyroid drugs to treat this condition.

Sometimes, hyperthyroidism starts during pregnancy because of small lumps (nodules) in the thyroid. These nodules make too much thyroid hormone.

The thyroid also can become overactive after childbirth. In the first year after giving birth, about 7% of women get postpartum inflammation of the thyroid. This problem starts with hyperthyroidism. 

  • Hypothyroidism:

A common cause of underactive thyroid in pregnant women is Hashimoto disease, sometimes called Hashimoto thyroiditis. This autoimmune disease occurs when your immune system forms antibodies (immune proteins) that attack the thyroid. This, in turn, causes the gland to make too little thyroid hormone. People with this disease may have symptoms of hypothyroidism or they may notice no effects.

Other causes of hypothyroidism include iodine deficiency, prior treatment for hyperthyroidism (when the thyroid makes too much thyroid hormone), and surgery to remove thyroid tumors.

What is the treatment for maternal hyperthyroidism?

During pregnancy, the preferred treatment for pregnant women with hyperthyroidism due to Graves’ disease is antithyroid medication. These drugs prevent the thyroid from making too much thyroid hormone. Temporary (gestational) hyperthyroidism does not need this treatment.

Pregnant women with Graves hyperthyroidism or thyroid nodules should start antithyroid drug treatment or, if already taking this medication, see their doctor about the dose. Hyperthyroidism due to Graves disease most often improves as pregnancy advances but may worsen during the first six months after birth. Therefore, your doctor may need to change your dose of antithyroid medicine both during and after pregnancy.

In the first trimester of pregnancy, the preferred drug to treat hyperthyroidism is propylthiouracil (PTU). Another antithyroid drug, methimazole, may cause birth defects if taken during early in pregnancy. Women may need to take methimazole in the first three months of pregnancy if they cannot tolerate PTU.

After the first trimester, experts recommend switching from PTU to methimazole. This is because in rare cases PTU can cause severe liver injury. Both drugs are equally effective. Talk to your doctor about the benefits and risks of these medicines, and which is the best choice for you.

Antithyroid medication can treat most cases of Graves disease in pregnancy. Rarely, some women may need surgery to remove part of the thyroid. The best time for this surgery during pregnancy is the second trimester (months 4 through 6).

Women who are or may be pregnant should not receive treatment with radioactive iodine. This radioactive drug usually destroys the patient’s thyroid gland to stop it from being overactive and can harm the unborn baby’s thyroid.

What is the treatment for maternal hypothyroidism?

Before pregnancy, it is important that thyroid hormone levels are normal both before and during pregnancy. If you are already receiving levothyroxine to treat hypothyroidism, you should have your thyroid hormone levels checked before you try to conceive. If your TSH levels are too high, you may need an increase in your dose of levothyroxine. You should delay pregnancy until your disease is well controlled.

During pregnancy, once a hypothyroid woman becomes pregnant, the levothyroxine dose often must increase. Possibly the dose must go up by as much as 30% or more in the first 4 to 6 weeks of pregnancy. Contact your doctor soon after you know you are pregnant, so you can get a thyroid function blood test and discuss your treatment plan.

Will your baby need special care?

Most people with Graves disease have measurable antibodies in their blood known as thyroid-stimulating immunoglobulins. In pregnant women with Graves disease, these antibodies can pass across the placenta to the baby. Though it does not occur often, this can cause thyroid disease and other medical problems for the newborn. All newborns of mothers with Graves disease who are positive for these antibodies should be checked for signs of thyroid problems and treated if necessary.

What can you do to help have a healthy baby?

You can help ensure both your baby’s health and your own health. Work with your pregnancy care provider and your endocrinologist, a specialist who treats hormone-related conditions, to receive proper medical care before, during, and after pregnancy. Take your medication as prescribed.

Your doctor can advise you on pregnancy planning. If you have active Graves disease, delay pregnancy until your disease is well controlled. Also, if you had radioactive iodine treatment, wait 6 to 12 months before trying to become pregnant.

Hypothyroidism and pregnancy 

The thyroid makes the hormones T3 and T4, which control metabolism, how your body uses and stores energy. When the thyroid does not make enough thyroid hormone, doctors call this underactive thyroid or hypothyroidism.

Hypothyroidism during pregnancy is not common. However, the symptoms can be overlooked because some mimic the hormonal changes of a normal pregnancy, such as tiredness and weight gain.

If left untreated, maternal hypothyroidism poses a risk for both mother and baby. A pregnant woman’s thyroid hormones are vital not only for her but also for the development of her baby. Pregnant women with uncontrolled hypothyroidism can get high blood pressure, anemia (low red blood cell count), and muscle pain and weakness. There is also an increased risk of miscarriage, premature birth (before 37 weeks of pregnancy), or even stillbirth.

About the author



Khurram Jamil - Digital Marketer By Profession & Blogger By Passion. Food Lover By Choice

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